The language centres of the telencephalon, i.e. the Broca's area and the Wernicke's area, are highly relevant as exam topics. The same goes for the structure of the limbic system and the basal ganglia.

00:00
Now within the multitude of connections that we saw in the previous slide, the connections can bedivided into a direct pathway as well as an indirect pathway. Both of these pathways aregoing to ultimately influence the state of the cerebral cortex. The direct pathway is the simplestone in that there are fewer connections. So this takes a more direct circuit route to influencethe cerebral cortex. Let’s take a look at the components of the direct pathway. First, this directpathway is going to stimulate or excite the motor cortex. This is how it goes about doing so.
00:49
Here we have the connection that exists between the striatum and the globus pallidus, so striatalpallidal. From the globus pallidus, we’ll have a connection here to the thalamus. Then from thethalamus, we can then excite the cerebral cortex. Then the cerebral cortex can communicate backwith its circuitry to the striatum. Now, what I want you to do now is to think about math.
01:25
The connections have been changed in color so that we have red and green. Red would beinhibitory influences, whereas green is an excitatory influence. We want to look at howthis direct pathway excites the cerebral cortex, so we’re looking at this communication or circuit,the circuit here and the circuit here. We want to think about math here to think about the fact thatthe direct pathway excites the cerebral cortex. For each red arrow, you’re going to have a minus one.
02:06
For this final green arrow, you'll have a plus one. Minus one times minus one is plus one.
02:14
Plus one times plus one is a positive or an excitatory influence. There’s also an indirectpathway between the basal ganglia to the cerebral cortex. Activation of the indirect pathway has anopposite influence on the motor cortex than does the direct. That’s because it will ultimatelyinhibit the motor cortex. Let’s look at the route or the circuitry here. We’re going to readilyappreciate, you'll readily appreciate the fact that this is an indirect route to the cerebral cortex.
03:00
Here you have the connection between the striatum and the globus pallidus. The circuit thenincludes a connection from the globus pallidus to the subthalamic nucleus and then back to theglobus pallidus specifically the internal segment, and from here to the thalamus, and then we caninfluence or inhibit the cerebral cortex. So, much more complicated circuitry here and then in theend, it has a negative influence on the cortex. The cortex does feedback on the striatum to kind ofcomplete this loop. Again, we’re going to think about math in coming to an understanding that thisis an inhibitory pathway upon the globus pallidus. And so now, the arrows have changed colorso that those that are inhibitory are red and those that are excitatory are green. Anything in redis a minus one. Anything in green will be a plus one. We have a minus one, a minus oneis a plus one. Plus one times a plus one here, because it’s excitatory is still plus one.
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Now, we have a negative one. A negative one times a positive one is now a negative one.
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Then a negative one times a positive one remains negative. Now we have a negative influenceon the cerebral cortex by just using simple math. Another pathway to bring to your attentionis that of the nigrostriatal pathway. We see this pathway between the substantia nigraand the striatum right in through here. This will modulate the direct as well as theindirect pathways. By doing so, it can ultimately excite the direct pathway. When that happens,you excite the cerebral cortex. Direct pathway excites, indirect inhibits the cortex.

About the Lecture

The lecture Direct and Indirect Basal Ganglia Pathway by Craig Canby, PhD is from the course Basal Ganglia. It contains the following chapters:

Pathways – Direct

Pathways – Indirect

Pathways – Nigrostriatal

Included Quiz Questions

Which of the following statements is CORRECT about direct pathways?

Globus pallidus internus has an inhibitory effect on the thalamus.

Dopamine inhibits the direct pathway

The inhibition of the globus pallidus by striatum also inhibits thalamus

The striatum has an excitatory effect on the globus pallidus internus

The direct pathway has an inhibitory effect on the cerebral motor cortex

An indirect pathway would result in disinhibition of which of the following?

Subthalamic nucleus

Substantia nigra

Putamen

Globus pallidus externus

Globus pallidus internus

Which of the following best describes the effect of dopamine on excitatory and inhibitory pathways of the basal ganglia?

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